until last week, eliza johnson was doing about three years in prison on a drug conviction. then she was suddenly set free. what is it like to be out of prison? >> free now. yay! i can breathe. >> reporter: free because of the bizarre alleged actions of this woman, former massachusetts chemist, annie duken. >> can you tell us what happened? >> reporter: the state of massachusetts is accusing her of tampering with drug evidence that could call into question at least 34,000 cases going back to 2003. 34,000. at the moment, she faces only three charges. however, in boston alone, the d.a. estimates as many as 500 convicted felons could be set free. how big of a mess is this? >> at this point, susan, we don't know. >> reporter: at this lab, now closed by the state, duken allegedly mishandled drugs seized by police for evidence at trial. she allegedly estimated the amount of drugs at times by simply looking at them, and certified some drugs as cocaine that are now testing negative. she didn't just write down the wrong thing. prosecutors accuse her of doctoring evidence to change te